High frequency oscillating circuit



1938. L. DE FOREST 2,126,541

HIGH FREQUENCY OSCILLATING CIRCUIT Filed Sept. 20, 1935 2 Sheets-Sheet 1INVENTOR.

Lee de Forest ATTORNEYS A11g- 9, 1938. L; DE FOREST 2,126,541

HIGH FREQUENCY OSCILLATING CIRCUIT Filed Sept. 20, 1935 2 Sheets-Sheet 2INVENTOR.

Lee d6 Fewest BY Ewan? ATTORNEYS Patented Aug. 9, 1938 UNITED STATESPATENT OFFICE HIGH FREQUENCY OSCILLATING CIRCUIT Application September20, 1935, Serial No. 41,410

17 Claims.

My invention relates to improvements in high frequency and ultra-highfrequency circuit con.- structions, and particularly for that range ofwave-length, known as ultra-short range, lying between or 12 meters and1 or 2 meters.

Particularly in the field of ultra-short-wave therapy or radio therapy,it has been found desirable to place at the physician's disposal apowerful ultra-short-wave oscillator, the wave- 10 length of which canbe readily and continuously varied within wide limits, for examplebetween 3 and 13 meters. I-leretofore the design of such continuouslyvariable oscillator circuits has depended upon the use of conventionalhelices with sliding contacts thereon, inducto-meters, or variablecondensers or a combination of both. Such arrangements present manymechanical difliculties and complications, and it is found that theeiiiciency of such oscillating circuit with lumped inductance andcapacity varies unduly as the natural period of such circuits is changedfrom maximum to minimum by means of varying said lumped inductance orcapacity.

It is well-known that the Lecher system of parallel conductors lendsitself particularly well to such high frequency oscillating circuits.The wave-lengths of such Lecher systems are practically identical withthe actual physical length thereof, which means that with wave-lengthseven as short as 3 or 4 meters the physical dimensions oi the systembecome impractically large.

I have found however that by coiling a pair of Lecher parallelconductors, either in the form of a spiral or of a helix, the advantagesof distributed capacity and inductance of the Lecher system aremaintained, while at the same time the physical overall dimensions ofthe system are very greatly condensed, so that such oscillating systemslend themselves very readily to the practical requirements ofultra-short-wave therapy and the like.

In the accompanying figures which illustrate several methods of applyingmy invention in 45 practical form,

Figure 1 is a schematic diagram of my invention comprising spiral Lecherconductors used as a wave meter;

Fig. 2 is a schematic diagram of an ultra short wave oscillatorembodying the spiral Lecher conductors of Figure 1, used as a therapydevice;

Fig. 3 is a modification of the system illustrated in Figures 1 and 2,in which helical Lecher conductors are used;

Fig. 4 is a detail of a mechanical construction of a Lecher spiral offlat ribbon conductors;

Fig. 4A is a detail of the structure of Figure 4 showing one of theinsulating rods;

Fig. 5 is an elevation of a system employing flat ribbon Lecherconductors constructed in accordance with Figs. 4 and 4A;

Fig. 6 is a fragmentary detail of the structure of Figure 5 showing thestructure as it appears when shaft l3 has been rotated somewhat morethan 90 clockwise from the position of Figure 5;

Fig. 7 is a plan view of a portion of the structure of Figure 5 showingthe spiral broken away at its inner end and omitting the insulatingsupports for the said spiral;

Fig. 3 is a fragmentary View of an alternative spiral Lecher system.

In Figure 1 I have shown a pair of parallel wires coiled in the form ofa spiral, the distance between the turns of which is larger than thedistance between the parallel wires constituting the Lecher conductors.I have shown a small loop 3 at one end of the system and joining the twoparallel conductors l and 2. The other two ends of the Lecher wires areshown open, although these may also be closed if desired. A slidingbridge 4 is shown bridging the two parallel conductors. When this systemis used as a wave meter I prefer to bring the loop end 3 into closeinductive coupling with the oscillating system whose wave-length it isdesired to measure, as is here shown where coil 33 and radio frequencyammeter form part of said oscillating system. With such an arrangementthe amount of current flowing in coil 33 as indicated at 39 will be moreor less varied when the bridge l is slid along the Lecher conductors toa point where the natural period of the closed Lecher system t, i, 3, 2,4 becomes that of the oscillations in the coil 33. Or instead of placingthe indicating instrument in series with the high frequency oscillatingcircuit, dip readings may also be obtained in a milliameter supplyingthe plates of the oscillating tubes which are exciting the coil 33, asis well known to those skilled in the radio art. Instead of reading theindication of a meter placed in the oscillator or supply circuit, theindication of resonance between wave meter and exciting circuit may beequally well obtained by the use of a glow tube 60, the terminals ll ofwhich are connected together by insulating arm H3 and are thus slidablealong conductors I, 2, so that they may be connected across any twoopposite points on the Lecher system, preferably midway between the loop3 and the sliding bridge 4 where exists a potential loop in the standingwave therein set up.

The same system of spiraled Lecher conductors above described I haveshown in Figure 2 as connected to the plates of a push-pull ultraaudionoscillation generator. Here the plate 8 of one oscillator tube is shownconnected to the grid I! of the other tube through a variable condenser9. In this Figure 2 I have shown the plate supply as being led to thesliding bridge 4 by means of a flexible conductor I00. However it isusually more convenient to supply the plates at a point where theconductors enter the audion tubes through radio-frequency choke coilsllli, IN. I have shown the sliding bridge 4 held in a slot 5 in theradial arm 5 which is pivoted at the center of the spiral formation atH, in such a way that when said arm is rotated around its pivot thebridge 4 is held in close contact with the two Lecher conductors and canthus be moved from the center to the outer periphery of the Lecherspiral. For this purpose a crank handle I at the end of the radial armaffords convenient means.

In this figure, I have shown the secondary circuit which consists, fortherapy purposes, of two insulated applicator pads 49, 49 as connectedto opposite points on the Lecher conductors l, 2, through the medium ofthe wiping contacts 4i 42 mounted on the insulating arm H3. The properlocation of these connection points obviously depends upon the positionof the shortcircuiting bridge 4 upon the Lecher system. There is anoptimum location for these secondary take-off points. When these arelocated too near the bridge 4 it is obvious that there will be onlysmall or no potential diilerence applied across the two applicator pads.On the other hand when the flexible cables leading to the applicatorpads are connected too close to the plates of the oscillator tubes thesecondary circuit is apt to absorb too large a load from the oscillatingsystem, causing the tubes to overload and to become undulyheated. I havefound that the optimum location of the slidable secondary contact points4|, 4| is roughly midway between the tube terminals of the Lecher systemand the short-circuiting bridge 4. However, these contact points maysometimes be advantageously located along the Lecher conductors wellbeyond the sliding bridge contacts.

In order to safeguard the patient against any possible shock from thehigh voltage applied to the plates of the oscillator, I prefer to insertstopping condensers B8, 88 in the leads from the Lecher conductors tothe applicator pads.

As an alternative to the above spiraled Lecher system I have shown inFigure 3 the two Lecher conductors while close together wound in theform of a helix. In the axis of this helix is shown a shaft I! overwhich slides a hub 45 carrying an arm 5 (preferably of insulatingmaterial) which carries at its end a sliding bridge 4 which shortcircuits the two Lecher conductors. which the hub 45 is keyed to permitsame to travel longitudinally along the shaft while it is being rotatedby means oi? the crank arm 5 and handle 1. Two ends of the Lecherconductors are again shown connected to the two plates of the oscillatortubes, as in Figure 2.

It is obvious of course that other types of oscillation generatorcircuits can be connected to the Lecher conductors in place of the push-At 8 is shown a longitudinal slit in pull ultra-audion arrangements hereshown, and I do not wish to be limited to any particular type of highfrequency oscillation generator. However the one here shown I have foundespecially efllcient and convenient as oscillating satisfactorily over awide range of frequencies, e. g., as represented by a wave-length rangein actual practice lying between I and I4 meters.

In Fig. 3 the secondary circuit, which may be identical with thesecondary circuit of Fig. 2, is shown connected to wiping contacts 4|,4|, which are arranged to move along the conductors I, 2, in unison. Inorder to effect this movement of the brushes an insulating sleeve isprovided, which sleeve is free to rotate on shaft i3. Carried by thissleeve, and spaced from each other by the large diameter portions El, 82thereof, are the three crank and commutator portions 56a, 58b and 55c.Each of the portions 55a and 561) carries an arm 55 on which is slidablymounted an arm 65 carrying a wiping contact 4| adapted to make contactwith a corresponding one of the Lecher conductors l, 2.

A connection is made, through the insulating sleeve, from the part 560.,to crank part 56c.

Since contacts 4i, arms 55, crank portions 55a, 56b and 560 are of metalthe brushes 4i bearing as they do on crank portions 561:: and 56c takeoif current to the secondary circuit, as indicated above.

It is clear from the above description of Figures 2 and 3 that theoperator may obtain a completely continuous change of frequencies as herotates the radial arm 5 and thereby causes the short circuiting bridgeto move over the entire length of the Lecher conductors from one end tothe other. With the push-pull ultraaudion circuit here shown I havefound it un-- necessary to vary the capacity of the grid couplingcondensers 9, 9 through any wide limits as the wave-length of the Lechersystem is changed from 3 to H meters; although for a certain length ofthe oscillating Lecher system the efficiency oi: the generator may beincreased by suitably varying said coupling condensers S, 9. Aconvenient way of effecting this is to have the two shafts of thesevariable condensers coupled mechanically together, but well insulatedfrom each other and to slowly vary the capacity of these condensers bymechanically coupling their shaft through a suitable train of gears or acam arrangement whereby the capacity of the condensers is varied as thearm 5, carrying the short circuiting bridge, is rotated.

In Figure 4 I have shown in detail a mechanical construction of a Lecherspiral which I have found particularly suitable to the ends in view. Iprefer to employ in place of a round conductor, a flat ribbon as shownhere which is wound in a spiral formation with the various turns of thespiral held rigidly in place through the use of spokes built up of shortsections of suitable insulating material, such as Isolantite, porcelain,glass or quartz rods. Bakelite, or similar plastic, or syntheticinsulators are quite unsuitable where large amounts of energy in thisrange of frequencies are to be employed. As shown in Figure 4 shortIsolantite rods, as shown in detail in Figure 4A, are nested end to endwith sections of the flat spiraled ribbon intermeshed between theopposing ends of the isoiantite rods. When thus assembled the Joints arecemented together with a suitable non-conducting cement, e. g., quartzcement so that the entire structure is held rigidly together.

Two such spirals as I have here shown are then mounted co-axially closetogether in parallel planes as shown in Figure 5. Through the center ofthese two spirals I locate an inner shaft l3 of insulating material, e.g., a quartz rod on which I rigidly mount two radial arms 55, 55. Thesearms are of metal. Each arm 55 carries a sliding collar 65 which in turncarries a suitable brush of spring material 4|, 4| adapted to travelover the outside edge or margin of each spiral ribbon as the arms 55 arerotated about the axis i3. Each arm 55 makes contact at the shaft i3with a wiping contact brush 45, 46 to which are connected the flexiblecables leading to the secondary or output circuit which in radio therapywork will be the applicator electrodes as shown in Figure 2 at 49, 49.

Surrounding the central insulating shaft I3 is a tube 23, preferably ofinsulating mamrial, in the center of which is mounted a radial arm 5. Onthis radial arm slides the short circuiting bridge 4 which is mounted onthe slide 45 so that as the arm 5 is rotated the brushes 4, 4 make closecontact with the sides or inner edges of the parallel ribbons I, 2 ofthe Lecher system and can thus travel from the inner to the outer endsof the Lecher spiral while the secondary contact brushes 4|, 4| can alsotravel over said spirals entirely independently of bridge 45.

In this Figure 5 I have shown the two plates of the oscillating tubes 8,8 connected to the outer ends of the two spirals.

Figure 6 shows more in detail the above described arrangement where theshort circuiting bridge 45 carries the two wiping brushes 4. 4 arrangedto traverse the inner edges of the two parallel spiral ribbons 2, whilethe secondary brushes 4|, 4| are attached each to its respective collar85 which slides along and makes contact with the conducting radial arms55, 55. The position of arms 55, 55. has been altered in Fig. 6 in themanner described above.

=Flgure 7 shows a plan view of the above arrangement. Here the metalarms 55 travel outside of the spiral ribbons to take off current to thesecondary circuit through the wiping contacts 46 while the insulatedlymounted arm 5 travels on the inner sides of the spiral ribbons andcarries the bridge 4 which short circuits the two parallel spiralribbons.

Instead of taking off energy to the secondary or load system from thesame Lecher conductors as constitute the primary oscillator which I haveabove described I might use 4 Lecher conductors, two close together forthe primary oscillating system and two parallel spiral conductors eachlying outside of but close to the primary Lecher conductors. Such anarrange- .ment I have shown fragmentally in Figure 8 where theconductors in place of being flat ribbons as shown in Figures 4, 5 and 6are shown as tubes or wires of circular or oval cross section. Here Ihave shown the short-circuitin bridge 45 with the two wiping brushes 4,4 as sliding over thetwo primary Lecher conductors and 2 and two brushes4|, 4| travelling over the two outside Lecher conductors I02. The

radial arm arrangement for sweeping the bridge.

45 around the spiral as well as the two insulated but mechanicallyconnected secondary brushes 4|, 4| are similar to the arrangementalready described in connection with the preceding figures.

I wish it understood that while the above described system isparticularly useful in ultrashort-wave therapy work the system may beequally well used for any radio application where it is desirable to beable quickly to sweep continuously through a wide range of frequencies.I do not wish therefore to be limited to application of this inventionto radio therapy purposes.

In my United States Patents 730,246, 730,247 and 730,819 all of June9th, 1903, I show for .the first time Lecher conductors as applied tocommercial wireless telegraph purposes, and for the first time twistedinsulated Lecher wire conductors. I also show these latter arranged inhelical formation. These twisted conductors are not strictly parallelconductors however, whereas in the present application I limit myself tostrictly parallel conductors, arranged in spiral or helical formations.

What I seek to secure by United States Letters Patent is:

1. An oscillating circuit containing distributed inductance and capacityconsisting of two parallel-insulated conductors wound in spiralformation, the distance separating the two parallel conductors beingsmall relative to the pitch of said spiral.

2. An oscillating circuit containing distributed inductance and capacityconsisting of two parallel insulated conductors wound in helicalformation, the distance separating the two parallel conductors beingsmall relative to the pitch of said helix.

3. An oscillating circuit containing distributed inductance and capacityconsisting of two parallel insulated flat ribbon conductors, wound incol] formation, the distance separating the conductors being smallcompared to the pitch of the coil.

4. An oscillating circuit containing distributed inductance and capacityconsisting of two parallel insulated fiat ribbon conductors in coilformation, the distance separating the conductors being small comparedto the pitch of the coil, and a wiping brush arranged to connect saidparallel conductors and to slide along them.

5. An oscillating circuit containing distributed inductance and capacityconsisting of two parallel insulated conductors arranged in coilformation with the distance separating the con ductors small comparedwith the pitch of the coil, a wiping brush arranged to connect saidconductors and to slide along them, and two additional brushes arrangedto wipe over said parallel conductors.

6. An oscillating circuit containing distributed inductance and capacityconsisting of two parallel insulated conductors arranged in coilformation with the distance separating the conductors small comparedwith the pitch of the coil, a. wiping brush arranged to connect saidconductors and slide along them, and two addi tional brushes arranged towipe over said parallel conductors, said additional brushes being movedtogether and independently of said wiping brush. v

7. An oscillating circuit containing distributed inductance and capacityconsisting of two par- 8. Two parallel Lecher conductors wound in spiralform with the distance between the conductors small as compared to thepitch of the coil, two brushes adapted to short circuit said conductorsmounted on an arm capable of being rotated about the axis of saidspirals, and two additional brushes adapted to complete connections toan external circuit each mounted on a radial arm, said radial arms beingmounted on a common shaft and designed to rotate about the axis of saidspiral.

9. A generator of high frequency electrical currents, two parallelconductors connected to said generator the conductors being wound in acoil with the distance between conductors small as compared with thepitch of the coil, a short circuiting brush adapted to be moved alongsaid parallel conductors, and two additional brushes insulated from eachother designed to be moved along said parallel conductors independentlyof the movement of the first brush.

10. A generator of high frequency electrical currents, two parallelconductors in coil formaticn with the distance between conductors smallrelative to the pitch of the coil connected to said generator, a shortcircuiting brush adapted to be moved along said parallel conductors, andtwo additional brushes insulated from each other designed to be movedalong said parallel conductors independently of the movement of thefirst brush, the location of said first brush determining thewave-length of the primary oscillating system and the other two brushesbeing adapted to be so located along the parallel conductors as tosupply the optimum amount of electrical energy to be taken from saidparallel conductors.

11. Two parallel Lecher conductors wound in spiral form with thedistance between conductors small relative to the distance between turnsof the spiral, two brushes mounted on an arm capable of being rotatedabout the axis of said spirals, two additional brushes each mounted on aradial arm, said radial arms being mounted on a common shaft anddesigned to rotate about the axis of said spiral, each of said brushesbeing connected through flexible conductors to a flat conductingsurface, said conducting surfaces forming an air spaced condenser.

12. An oscillating circuit containing distributed inductance andcapacity consisting of two parallel insulated conductors wound in acoil, the distance separating the parallel conductors being smallrelative to the pitch of the coil windings, a wiping brush parallel to aradius of said windings arranged to connect said parallel conductors andto slide along them, and means for supplying electrical oscillations tosaid 05- cillating circuit.

13. An oscillating circuit containing distributed inductance andcapacity consisting of two parallel insulated conductors arranged inhellcal formation with the turns of the helix widely spaced relative tothe spacing of the conductors, and a wiping brush arranged to connectsaid helical conductors and to slide along them.

14. An oscillating circuit containing distributed inductance andcapacity consisting of two parallel insulated conductors wound. inhelical formation with the turns of the helix widely spaced relative tothe spacing of the conductors, a wiping brush arranged to connect thetwo parallel conductors and to slide along them, and a radial armrotatably mounted on the axis of the helix, said arm being free to moveaxially whereby said brush travels radially along the helix as the armis rotated about the axis of the helix.

15. An oscillating circuit containing distributed inductance andcapacity consisting of two parallel insulated conductors wound inhelical formation with the distance between conductors small relative tothe distance between turns of the helix, a wiping brush arranged toconnect the two parallel conductors and to slide along them, said brushbeing mounted on a radial arm rotatably mounted on the axis of the helixsaid arm being adapted to travel along the axis as it is rotatedthereabout.

16. Two parallel Lecher conductors wound in a helix with the distancebetween the conductors small as compared with the pitch of the helixyashort circuiting brush mounted on an arm rotatable about the axis of thehelix and movable along the axis when rotated, and two additionalbrushes adapted to complete external connections each brush beingslidably mounted on an arm rotatable about the axis of the helix saidarms being connected for rotation together.

17. Two parallel Lecher conductors wound in helical form with thedistance between conductors less than the distance between turns of thehelix, two brushes mounted on an arm capable of being rotated about theaxis of the helix, two additional brushes each slidably mounted on anarm capable of being rotated about the axis of the helix, each of saidlast mentioned brushes being connected to a fiat conducting surfacecomprising one of the plates of an air spaced condenser.

LEE m FOREST.

